1. Technical Field
Embodiments of the present invention relate generally to cryosurgical equipment, and, more particularly, to cryosurgical treatment methods and devices with enhanced heat transfer between an external surface and internal fluid cryogen.
2. Description of Related Art
Cryoprobes that “boil” a liquid cryogen, when this liquid cryogen is supplied from an external source into the cryoprobe, are known for performing cryosurgical procedures. Generally, a cryogen is delivered into a cryoprobe in the form of two-phase fluid. This is caused by the fact that a certain fraction of the liquid cryogen is evaporated inevitably on the way to the cryoprobe as a result of imperfect thermal insulation of the delivery hose. The cryogen two-phase condition cannot be improved by separating between the liquid and gaseous phases completely in the internal cavity of the cryotip (the distal section of the cryoprobe) without application of special measures. In addition, in particular for the use of nitrogen as a cryogen, the liquid nitrogen interact with solid warmer surface by creating nitrogen gas cushion, known as Liedenfrost effect, thus reduce considerably the ability to absorb heat from the warmer surface. Without such special means, it is impossible to completely use the liquid fraction of the cryogen for effective freezing of a treated tissue, forcing the partial change of phase of the fluid cryogen to take place as close as possible to the targeted surface.
Solutions to this problem are known. For example, U.S. Pat. No. 4,726,194 features a conduit with active heating thereof through which liquid nitrogen flows. The conduit terminates in an expansion chamber that is filled with cotton wool, in order to expand the volume available for boiling.
Another example is U.S. Pat. No. 4,082,096, which features a deformable mass that receives liquid cryogen, surrounded by a membrane that is impervious to liquid nitrogen.
Other examples include U.S. Pat. Nos. 5,520,682, 6,565,556, 4,946,460, 7,189,228 and 5,674,218, each of which features an expansion chamber.